Each usergroups have your own label, you just need to find the labels and use the similar code provided above to replace different group titles with different pictures. 

jQuery('.wc-comment-label').html('<img src="your image URL"/>');

You need to do right-click(or CTRL+F12) then Inspect element on the frontend page to find each selector.

Please note you should change the red mark code for each usergroups.

Please precize - "in your current active the js files"

It will replace all labels with one particular picture or i can replace differnet group titels with different pictures?

Please follow the steps below.

Put the following JS code in your current active the js files:

1.For wpDiscuz:

jQuery('.wc-comment-label').html('<img src="your image URL"/>');

2. For wpforo:

jQuery('.wpf-member-title ').html('<img src="your image URL"/>');

Also please navigate to the Dashboard > Forums > Settings > Styles admin page put the following CSS code in the "Custom CSS code" textarea:

#wpforo-wrap .wpf-member-title.wpfut{
   border: none !important;
}
.wpfbg-6 {
   background-color: inherit !important;
}
.wpfcl-3 {
   color: #777777 !important;
}

Please note: The red marked value should be you image URL